1. Field of the Invention
The invention relates to a pair of scissors with two shanks joined to one another via a pivot joint, in particular hairdressing shears.
2. Prior Art
Known scissors operate with cutting edges that move about a common, fixed pivot point relative to one another. In the process, the cutting edges slide on one another so that they touch at point (the cutting point).
When the scissors close, the cutting point moves out from the common pivot point of the scissors in the direction toward the tip of the scissors.
In this process, the opening angle of the scissors, that is, the angle of the cutting edges converging on one another, also changes.
Filament-like material to be cut, such as hair, depending on the opening angle, edge sharpness, and so forth, slides more or less far in front of the actual cutting point until it begins to be cut, is held, and then severed. Since in this cutting method, the material to be cut does not execute a defined rolling motion about its longitudinal axis, necessarily only a partial cross section of the material to be cut is actually cut, while the rest is virtually pinched off or torn off.
Poorly cut hair is finally the starting point for subsequent damage and can cause splitting, among other effects.
The object of the invention is to cut filamentary material to be cut, especially hair, uniformly over its circumference and cross section without any zones of pinching and tearing.
According to the invention this object is attained by a scissors comprising two shanks pivotally connected to each other at a pivot joint; respective longitudinally extending blades for cutting the filamentary material attached to a corresponding shanks and means for vibrating at least one blade in the longitudinal direction, which comprises an electrically powered vibrator. Accordingly, at least one shank can be made to vibrate parallel to the longitudinal direction of this shank by means of the electrically powered vibrator.
The invention has the advantage that filamentary material to be cut, in particular hair, can be cut uniformly over its circumference and cross section without pinching and tearing zones. With the scissors of the invention, the hair slides between the cutting edges while it is being cut through. In the process it is reliably and uniformly severed. When the scissors are closed, the axially oscillating motion component that is additionally superimposed on at least one cutting edge leads to improved cutting properties.
Further advantageous features of the invention are described hereinbelow.
Good cutting results are attained if the vibrator includes a piezoelectric travel transducer, which is located between the blade and an end of the shank toward the handle, and connects the blade and the end of the shank. The oscillating motion is determined by the frequency and amplitude at which the piezoelectric travel transducer vibrates.
The oscillating motion should be executed at such a high frequency that during normal use of scissors, the hair rolls over its circumference on the cutting edges at least once during the cutting operation.
The amplitude of the vibration depends on the circumference of the hair. The initial amplitude value can be approximately 100 to 200 xcexcm.
If both cutting edges vibrate simultaneously with phase-offset from one another, then half the amplitude suffices.
A system with adjustable amplitude and frequency for different material to be cut is thus possible.
The piezoelectric travel transducer can be operated at an ultrasonic frequency. It is integrated into at least one cutting edge. In a manner analogous to an ultrasonic cleaning sonotrode or a welding sonotrode, the longitudinal wave is transmitted along the cutting edge. The vibration generator, which in the final analysis is mechanical, may be disposed on the side of the cutting edge or strut of the scissors. If on the side of the strut, corresponding mechanical play at the bearing point would have to be considered. This applies equally to other vibrators on the strut.
The system is triggered electrically by an ultrasonic generator, which is coupled via electrical connecting cords to the electromechanical vibrator.
Good cutting results are also attained if, as the vibrator, an eccentric washer that surrounds the nail of the joint is provided; if the eccentric washer is inserted into a round recess in the shank and is rotatably joined to the nail; and if a miniature motor is provided for rotating the eccentric washer about the nail. To that end, a standard connecting nail is replaced with an electromechanically driven eccentric unit. The axial component of the eccentric motion leads to the desired cutting motion. As the drive for the eccentric unit, a miniature motor is sufficient and has the advantage of not making the scissors harder to manipulate.
The vibrator can also be embodied such that the shank at least in some regions comprises a magnetostrictive material, and a rigid, stationary exciter coil is wrapped around this material. The cutting edges of the scissors are mounted here on a base body of magnetostrictive material. By applying an electromagnetic field to the magnetostrictive material, a change in length of the material and finally an oscillation of the cutting edges relative to one another are brought about. The exciter coils may be disposed in the strut region of the scissors. The exciter coil is connected to a generator via an electric connecting cord.
Nickel or a nickel alloy is suitable as the material. First, nickel has the required magnetostrictive properties, and second, nickel steel is very highly suitable for manufacturing scissors. To prevent contact allergies, the material may have a plastic coating.